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    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
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  <body>
    <script>
     // 输入：[1, 2, 3, 4], 10
     // 输出：[10, 1, 2, 3, 4]
      let arr = [1, 2, 3, 4];
      let item = 10;
      let newarr;
      function prepend(arr, item) {
        newarr = [item];
        newarr.push.apply(newarr, arr);
        return newarr;
      }
      prepend(arr, item);
      console.log(newarr);
    </script>
  </body>
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